This study focuses on clarifying the impact of the postponement of career decision-making after high-school graduation on life satisfaction among late adolescents, employing heterogeneous treatment effect analysis. Using the Korean Children and Youth Panel Survey (KCYPS), 1,629 high-school graduates were analyzed to address the determinants of the postponement of career decision-making in order to estimate propensity scores. With the propensity score analysis, stratification-multilevel method for heterogeneous treatment effect hypothesis was conducted. Heterogeneous treatment effect hypothesized that there would be much stronger association between life satisfaction and the postponement of career decision-making among the group who were more likely to postpone their careers after high-school graduation than among other groups. The results showed that adolescents who are men, graduated vocational high schools, have no college aspiration, and live in urban areas were more likely to postpone their decision-making on careers than their counterparts, respectively. And the postponement of career decision-making was negatively associated with life satisfaction among late adolescents and particularly the negative effect was stronger among the group showing higher propensity scores of being treated into the postponement of their career. The policy implications are addressed based on the research findings.